Okay, so this is entirely new to me. Sparrow is was an email client for Mac OS X and iOS (and Windows), which brought a decent Gmail experience to these platforms - as opposed to Apple's own not-so-good Gmail support and Google's Gmail iOS application which, well, is just a webpage. Google has now acquired Sparrow, and basically all hell has broken loose, to the point of Rian van der Merwe writing that 'we' lost "faith in a philosophy that we thought was a sustainable way to ensure a healthy future for independent software development, where most innovation happens".

Other than browsers which make money when a user searches, how many successful consumer software products do you know that are open source?

Virtually all web services run on, use or are built with open source software. Facebook, Google, Twitter, and a gazilion others - all consumer products. Then there's browsers (as you mentioned), Android (massive success story if there ever was one), Linux (powers god knows how many consumer products) - and this is just what I can think of without trying.